Kitty Empire, Observer pop critic

Last week, Glastonbury supremo Michael Eavis griped that booking the Wombles to play the legendary pop festival had been a mistake. Fur flew. Well, perhaps that's an exaggeration. Fur was certainly ruffled. Beards – both Eavis's and Uncle Bulgaria's – were probably tugged a bit hard. In the end, though, the Wombling will go ahead as planned next Sunday and I believe that it was all something of a cunning smokescreen; that this squall in a milk churn should have raged over a far more pernicious presence at Glastonbury. No, not the people that nick tents. Not the unicycle-riding jugglers in period costume: after all, they practice all year to display their colourful lifestyles to the straighter types who enjoy buying into it for one weekend. They deserve our indulgence.

No, I'm talking about Friday's headliners U2. Pompous, billowing, self-important, safe U2. At the very least, booking the biggest rock band in the world shows a distinct lack of imagination from a festival that has, in the past, thrown some eclectic curveballs round Worthy Farm's pasture land. Jay-Z in 2008: now that was a master-stroke.

More significantly, there are protests planned this year by a group targeting the Irish band's status as partial tax exiles. In 2006 the band moved some of their financial operation to the Netherlands. This state of affairs not only deprives their recession-ravaged homeland of funds, but lays bare a central hypocrisy at the heart of U2. Bono's global activism – much of it very creditable – rings a little hollow when this rock colossus pursues tax avoidance strategies more typical of a cut-throat business than a band of allegedly uplifting do-gooders. Not very in tune with the Glasto "vibes", wouldn't you agree?

Dorian Lynskey, critic and author of 33 Revolutions Per Minute: A History of Protest Songs

Firstly, U2 are the "safe" choice? Hmm. The fact we're having this debate suggests quite the contrary. In fact, the last time a Glastonbury headliner inspired as much controversy was Jay-Z. His set was so riveting because he had something to prove and a barrage of flak to overcome. U2 also have a great deal at stake, albeit for different reasons, and I expect them to come out with all guns blazing.

Glastonbury headliners are most exciting when they approach the festival with a sense of occasion and jeopardy rather than the sleek professionalism of a band doggedly working the festival circuit to plug a new album. Other A-list acts on the Eavis wish list, chiefly Prince and the Rolling Stones, have taken bigger pay cheques from rival events but this is U2's first festival appearance since the 1980s. Negotiating this kind of one-off is exactly when Glastonbury shines. U2's music may not be your bag but it's not as if the Friday night slot would otherwise be set aside for Animal Collective or Burial. It's a time for big-hitting rock acts and I'd rather have U2 than almost any of their arena peers. They have the hits, the stagecraft and experience to make this remarkable.

So much for the music. Now for the politics. Let's agree that the tax avoidance was a bad move in 2006 and an indefensible one now, and the Art Uncut protest is valid. But when did we start vetting festival acts over their financial affairs? And why only U2? Beyoncé played a concert for Said Gaddafi. Should she be on a Glastonbury blacklist too?

KE We are just going to have take Beyoncé's word that she donated her fee to charity, aren't we? It's a fair point that once you start examining the cash-flow of successful musicians, the sight is rarely edifying. But Beyoncé doesn't spend her spare time wagging her finger at world leaders over debt in the developing world. It is U2's hypocrisy that really rankles.

Much as it would amuse both of us, I'm sure, to see some left-field darling in a headline slot, I agree that it's fatuous to suggest that Eavis junk U2 for Gang Gang Dance. You need an act with a vast reach, of course, but you want some wow factor too. only fair to note that high-octane festival booking is a dark art, and that the reunited Pulp, say, might not have been on the table at the time the Eavises opened negotiations for this year's festival bill. But surely Pulp would have been perfect, providing an unexpected coda to their own Glastonbury moment back in 1995, when the sound of festival-goers singing "Common People" took them from indie darlinghood to something far greater? Or Amy Winehouse. With her track record, her handlers probably didn't want Amy on such a big stage in the UK so early on in her comeback. But she played in London last week before a dozen European festival dates. These are just two examples of artists who have great presence and real meaning and a sense of humour as well as mass appeal, all of which you would want in a memorable Glastonbury headliner. I'm afraid that U2 are the embodiment of "sleek professionalism" rather than Pyramid Stage legends in the making.

DL We could debate U2's finances till the cows come home to Worthy Farm, but we're talking about headlining a music festival, not heading a UN task force. That said, I'll take the point about apparent hypocrisy while responding that the only reason U2 invite such scrutiny, and are held to such high ethical standards, is that for the last 30 years they have campaigned passionatelyfor causes (including Amnesty, Greenpeace and CND) that are dear to Glastonbury's heart. A free pass? Not at all. But not something to be waved aside either.

Quibbling with Glastonbury line-ups is a great British pop tradition, up there with moaning about the Mercury Prize, and I'm not above it myself. I'm touched by your faith in Amy Winehouse, although after seeing her dispiriting turn at Bestival three years ago I wouldn't trust her to headline a local council fun day. And even if she pulls a Lazarus act, she, like Pulp, has been here before. More exciting, surely, to book big-name Glastonbury virgins, whether U2 or Bruce Springsteen or Jay-Z? I've seen many kinds of triumph at Glastonbury: the young band that rises to the occasion; the legends who reunite to waves of tearful affection; the gamble that pays off. The one that's surprisingly rare is the headliner with a back catalogue of songs that are part of the common language of pop. You don't have to be a U2 devotee to consider hearing the likes of "One" and "Where the Streets Have No Name" on the Pyramid Stage a good night out. Presence, meaning and a sense of humour are in the eye of the beholder but I've seen U2 hold unprepossessing sports stadia in the palm of their hand. I honestly can't see U2 failing to hold Glastonbury's attention.

KE Bruce Springsteen? Now you're air-punching! I take your point about the allure of a first-time Glastonbury exclusive, and grudgingly concede that Pulp are playing just about every other festival under the sun. And we can definitely agree on Bruce: big anthems, vast reach, plenty of heart, brilliant light and deep shade. But strangely, he didn't go down too well two years ago (as you will remember).

We could bat names back and forth until the cows evolve a fourth stomach. Here's one more just for fun: I saw U2 in a vast sports arena in Italy in (coughs) 1986, supported by Big Audio Dynamite, and BAD blew them offstage. Something is very askew if Mick Jones' sensational post-Clash outfit are playing two bands below Crystal Castles on The Other Stage.

I've been examining my conscience to pinpoint why I find the spectacle of U2 so tiresome and hollow. They say a cynic is just a frustrated romantic, and I have to confess I am a former fan who moved on. You're right, they have done sterling work for excellent causes; shining a spotlight on war-torn Sarajevo was an inspirational thing to do. More than any other band their size, they have tinkered with the tone of the stadium rock experience, from their Zooropa tour onwards.

But for all U2's efforts to deconstruct themselves in the 90s, I still feel they are this hegemonic force, to which all rock now feels it must aspire. The Edge's chiming guitar sound has been aped by just about every other big band out there – Coldplay, Kings of Leon, the Killers. And although their songs are often About Stuff, U2 patented this stubbornly pervasive tone of wafty, inchoate, non-specific, quasi-spiritual yearning that has come to typify big stadium acts. People like it because this generic yearning is so all-embracing, it can provide a fit for whatever longing is foremost in the listener's emotions. I guess I like my rock more hard and fast.

DL On that we're agreed. My heart sinks whenever a promising band eyes up the sports venues, sets the dial to "anthemic" and becomes a blustering bore. But I don't blame U2 for, say, the second Glasvegas album any more than I blame Nirvana for Nickelback. In fact, the inverse is the case. Every time an imitator gets it wrong, I'm reminded how often U2 get it right, and despite my usual inclinations. It's because, as a rule, I'm deeply suspicious of stadium shows and broad-brush sentiments that U2 always surprise me as a live act. It shouldn't work – indeed, occasionally it doesn't – but when they're on top form they hit a vein of emotional intensity and intimacy that leaves me wondering how they pulled it off. We know they can supply those vast, communal hits that have an almost primal attraction on the Pyramid Stage; less noted is the combative quality (think Achtung Baby) which throws the phones-in-the-air moments into sharp relief.

Of course, this debate won't be settled by us the two of us but on the stage itself, in front of the devoted, the curious, the sceptical and the outright hostile. Here's the world's most successful live band moving outside their comfort zone and needing to prove themselves to an audience that could go either way. However it goes down, that should be something to see.